1. Field of the Invention
The present invention relates to a processing apparatus for measuring performance monitoring parameters in transmission equipment, and particularly, to a processing apparatus for measuring performance monitoring parameters with improved accuracy in detecting transmission signal errors.
2. Description of the Related Art
Standardization of performance monitoring (PM) has resulted in G.826 and other recommendations formulated by the International Telecommunication Union--Telecommunication Sector (ITU-T), which provide common definitions for signal quality management in transmission paths. In actual error performance measurements, transmission equipment monitors incoming bit streams to detect performance anomalies and defects (e.g., bit errors), collects error data on some prescribed criteria, and reports the statistics of the detected errors, called "PM parameters."
FIG. 10 is a block diagram which shows a typical configuration of a conventional PM parameter processing unit, which is composed of the following main functional blocks: a failure detection unit 102, a PM controller 103, a counter unit 104, and a control signal generator 105. Reception signals carried over a transmission line 101 are monitored by the failure detection unit 102, which comprises a CV detector 102a and an LOS detector 102b. The CV detector 102a detects "Code Violation" (CV) errors in the reception signals, while the LOS detector 102b detects "Loss of Signal" (LOS) conditions. CV errors include bit errors, for instance, and LOS means the absence of reception signals lasting for a prescribed period. The detected CV errors are sent to an "Errored Second" (ES) detector 103a and a "Severely Errored Second" (SES) detector 103b disposed in the PM controller 103, as well as to a "Code Violation-Line" (CV-L) counter 104a in the counter unit 104. Likewise, the detected LOS condition is sent to the ES detector 103a and SES detector 103b in the PM controller 103, an "LOS Second-Line" (LOSS-L) counter 104b in the counter unit 104, and the control signal generator 105. The CV-L counter 104a counts the occurrences of CV errors. The LOSS-L counter 104b measures the duration of LOS conditions in seconds. The ES detector 103a sends an ES-L indication signal to an ES-L (Errored Second-Line) the counter 104c in the counter unit 104, when one or more CV errors have been observed in a predetermined time period or when an LOS condition has been detected. The ES-L counter 104c measures the duration of this ES-L indication signal in seconds. The SES detector 103b sends an SES-L indication signal to a "Severely Errored Second-Line" (SES-L) counter 104d in the counter unit 104, when 45 or more CV errors have occurred within a predetermined time period or when an LOS condition has been detected. An SES-L counter 104d measures the duration of this SES-L indication signal in seconds.
The control signal generator 105 watches the LOS detection signal, and when an LOS condition is detected in a certain time segment, it generates a control signal for that time segment. The control signal generated as such is supplied to the CV detector 102a so as to stop its operation. The next section will describe the details of this process, with reference to FIG. 11.
FIG. 11 is a timing diagram which describes the operation of the conventional PM parameter processing unit of FIG. 10, which specifically shows (A) time segments, (B) lower layer failures, (C) upper layer failures, (D) LOS condition, (E) the number of lower layer failures, and (F) failures detected by the CV detector. Note that the time axis is divided into 1-second time segments (A) and some elements in the PM parameter processing unit operate on this segmented time basis.
This timing diagram of FIG. 11 assumes that some lower layer failures (B) have happened, and thus the LOS detector 102b has detected some LOS conditions. The LOS conditions, which mean the absence of the reception signal, derivatively cause bit errors to be sensed by the CV detector 102a. As a result, some upper layer failures will be detected as indicated by the upward arrows (e) and (f) in FIG. 11. Although the upper layer failures (C) seemingly include many error indication pulses, only five pulses (a), (b), (c), and (d) represent the true bit errors independent of the LOS conditions, while the others are false errors derived from the LOS conditions. In such a case, the CV detector 102a has to detect only those genuine errors (a), (b), (c), and (d), but not the false ones (e) and (f). In reality, however, the CV detector 102a is unable to discriminate the false failures by itself. If the CV detector 102a signaled all those failures without discrimination, the counter unit 104 would accumulate the upper layer failures erroneously, and thus the resultant PM parameters would exhibit much larger values than the true values.
The conventional processing unit employs the control signal generator 105 that produces an appropriate control signal to avoid the above-described problem. In the present context shown in FIG. 11, the control signal generator 105 recognizes the presence of LOS conditions (D) from the output of the LOS detector 102b. It should be noted here that this LOS recognition is conducted on the basis of the predetermined time segments (A). More specifically, the control signal generator 105 drives its control signal output to "1" to disable the CV detector 102a, when an LOS is detected in each time segment (e.g., 1 second). In turn, it resets the signal to "0" when no LOS condition is observed. Meanwhile, the number of upper layer failures detected by the CV detector 102a in each time segment is indicated in (E) of FIG. 11. The CV detector 102a, however, does not always output the number of upper layer failures (E) as is, but it masks all failures in the time segment when the control signal with a value of "1" has been received from the control signal generator 105. Only when the control signal is "0," the CV detector 102a reports the number of detected upper layer failures as originally is. As shown in (F) of FIG. 11, the CV detector 102a indicates no failure in the first three time segments (1) to (3) due to the failure masking operations by the control signal generator 105.
In this way, the conventional PM parameter processing unit avoids the problem of false failure detection. However, there arises a side effect that the processing unit may fail to detect some true upper layer failures, such as (a), (b), and (c), which must be detected by the CV detector 102a. This is because the control signal generator 105 produces the control signal on the basis of discrete time segments, and the control signal masks all upper layer errors regardless of "true" or "false," within the time segment in which an LOS condition is observed. Accordingly, the counters in the counter unit 104 are unable to correctly accumulate the values of PM parameters.
The errors in the counter values obtained from the counter unit 104 could be compensated for by applying some appropriate firmware processes. However, it is desirable to seek a more accurate, hardware-based way of measuring the PM parameters, not to increase the workload imposed on the firmware.